In order to obtain high-temperature gas containing no impurities, it has been general to use an electrothermal type heating apparatus using an electric heater or an indirect regenerative type heating apparatus using a regenerative tube.
However, in the electrothermal type heating apparatus, a start-up time is long because heating elements must be prevented from being disconnected, and this type of heating apparatus is therefore practically inconvenient.
Further, the heating apparatus using a tube type regenerator is inferior in the effectiveness of regenerator, and it is difficult to product this type of heating apparatus having practical material and structure in order to obtain gas having a high temperature of approximately 1000 to 1600.degree. K.
In these prior art heating apparatuses, a time for which the high-temperature gas can be supplied is short, and there is a problem such as that a preparation time for making it possible to supply the high-temperature gas is long. Furthermore, fluctuation in temperature is disadvantageously large because the temperature suddenly drops.